The present invention is directed to a lamp assembly and, more specifically, to a lamp assembly that incorporates optical feedback.
Recent advances in light emitting diode (LED) technology has led to the development of several high-brightness LED lamps for use in automobiles and other applications. Many of these applications require a substantially white colored illumination when providing light for tasks such as, for example, reading a map or book. A common method of producing white light using LEDs is to deposit a yellow phosphor on top of a InGaN Blue LED die. Some of the blue light emitted by the LED is absorbed by the phosphor causing it to emit yellow light. The combination of the blue light from the LED and the yellow light from the phosphor combines to produce a metameric white light.
This technique is relatively simple and leads to a single component solution. However, this technique relies entirely on an InGaN emitter as the source of energy for the illuminator. Currently, most InGaN LED systems are less efficient and more expensive than other alternatives, such as AlInGaP LED emitters. As such, a system that relies primarily on an InGaN die, as the source of optical radiation, is typically more expensive to produce. Additionally, the use of a phosphor typically shortens the useful life of the device as an illuminator. This is because the phosphor typically decays at a faster rate than the underlying InGaN die. Additionally, as the phosphor decays, the relative proportion of yellow light emitted is reduced, which results in a color shift in the light output.
Another technique for producing white light is to combine the outputs of an amber AlInGaP LED and a blue-green InGaN LED in appropriate proportions. Such an approach is outlined in U.S. Pat. No. 5,803,579 entitled, ILLUMINATOR ASSEMBLY INCORPORATING LIGHT EMITTING DIODES, to Turnbull, et. al., commonly assigned with the present invention, and hereby incorporated by reference. Using this approach, the outputs of the LEDs are combined in different proportions to produce white light of different color temperatures. An increase in the proportion of amber light (or a corresponding decrease in the proportion of blue-green light) will produce a warmer white light corresponding to a lower color temperature. An increase in the proportion of blue-green light produces a cooler white light corresponding to a higher color temperature.
Although the two types of LED dies decay at a rate that is more similar than the rates of InGaN die and phosphors, the AlInGaP and InGaN dies still exhibit a difference in decay rates. These differences in decay rates lead to a difference in color temperature over the life of the device. However, since a change in relative proportion of one of the constituent colors still produces a resultant color, which is typically accepted as white light, the severity of this effect is acceptable in many applications. Unfortunately, this effect is typically increased due to the wide variance in intensity and somewhat lesser variance in color that is typical of modern LED production. In order to accommodate for intensity and color variance, one must measure the output of the blue-green and amber LEDs and adjust their initial proportions during assembly of the lamp.
Yet another method of creating white light using LEDs is to combine the colors of three or more LEDs in a particular ratio to form white light. A typical system may combine light from red, blue and green LEDs to form an RGB system that is capable of producing not only white light but any other color of light as well (by adjusting the intensity of the red, blue and green LEDs, independently). Another advantage of such a system is the potential for an improved color rendering index and thus an increase in the brilliance of colors on the object being illuminated. The primary difficulty in implementing an illuminator using a plurality of LEDs, especially where there are three or more colors, is accommodating the large intensity variance present in modern LEDs. The high variance in intensity of the individual color LEDs leads to wide variance in the output color. To solve this problem, LEDs are typically sorted by color and intensity. Frequently, further measurements of individual assemblies are needed to insure accurate color calibration. These methods may partially correct an initial problem but do not solve problems associated with differential brightness decay, which occurs with aging or changes in intensity of the individual constituent colors which can occur with changes in temperature of the die or the ambient environment.
As such, an illuminator assembly that adapts to light source component variability, to produce a desired resultant hue of illumination, is desirable.
An embodiment of the present invention is directed to an illuminator assembly that produces light of a desired resultant hue. In one embodiment, the illuminator assembly includes a processor, a memory, a plurality of light sources and a detector. The memory is coupled to the processor and stores data and information. Each of the plurality of light sources are coupled to the processor and produce a different primary color. The processor is capable of independently controlling the intensity of each light source so as to produce a desired hue resulting from the mixing of the light emitted from each light source. The detector is also coupled to the processor. The detector provides the processor with information, which the processor utilizes in determining how to adjust the intensity of each of the light sources to provide the desired resultant hue.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.